A conventional driving apparatus for a three-phase alternating current (AC) motor includes an inverter circuit, which outputs a three-phase alternating current to a three-phase AC motor and a control circuit, which controls the inverter circuit, for example as disclosed in JP 2563226.
Such an inverter circuit has six transistors. The six transistors will hereinafter be represented by SW1 to SW6.
The transistors SW1 and SW4 are connectedirectly to each other between a positive-pole bus and a negative-pole bus. The transistors SW2 and SW5 are connected directly to each other between the positive-pole bus and the negative-pole bus. The transistors SW3 and SW6 are connectedirectly to each other between the positive-pole bus and the negative-pole bus. The transistors SW1, SW2 and SW3 are connected to the positive-pole bus. The transistors SW4, SW5 and SW6 are connected to the negative-pole bus.
A common connection point of the transistors SW1 and SW4 is connected to a W-phase coil of a stator coil of the three-phase AC motor. A common connection point of the transistors SW2 and SW5 is connected to a V-phase coil of the stator coil. A common connection point of the transistors SW3 and SW6 is connected to a U-phase coil of the stator coil. The stator coil is provided by a star connection of the U-phase coil, the V-phase coil and the W-phase coil. A positive electrode of a direct current (DC) power source is connected to the positive-pole bus of the inverter circuit. A negative electrode of the DC power source is connected to the negative-pole bus.
An electric current sensor for detecting three-phase AC currents output from the inverter circuit is connected between the positive-pole bus of the inverter circuit and the positive electrode of the DC power source. The control circuit controls the six transistors such that switching operation of the six transistors is performed on the basis of the electric current values detected by the electric current sensor. In association therewith, the inverter circuit outputs three-phase AC currents to the three-phase AC motor from the three common connection points based on a difference in voltage between the positive-pole bus and the negative-pole bus.
When the transistors SW1, SW5 and SW6 are ON among the transistors SW1 to SW6, a W-phase electric current flowing from the inverter circuit to the W-phase coil is detected by the electric current sensor.
When the transistors SW2, SW4 and SW6 are ON among the transistors SW1 to SW6, a V-phase electric current flowing from the inverter circuit to the V-phase coil is detected by the electric current sensor.
When the transistors SW3, SW4 and SW5 are ON among the transistors SW1 to SW6, a U-phase electric current flowing from the inverter circuit to the U-phase coil is detected by the electric current sensor.
The control circuit uses the W-phase electric current, the V-phase electric current and the U-phase electric current detected by the electric current sensor as described above as the three-phase AC currents and controls the three-phase AC motor through the inverter circuit based on the three-phase AC currents.